JSFiddle - React, Tailwind, and code Playground

HTML

<body>
        <div class="wrap clearfix">
           <h1>Текст Текст Текст Текст Текст Текст Текст</h1>
            <div class="line"></div>
        </div>
    </body>

CSS

.clearfix {
  *zoom: 1;
}
.clearfix:before,
.clearfix:after {
  display: table;
  content: "";
  line-height: 0;
}
.clearfix:after {
  clear: both;
}

.wrap {
    width: 400px;
    border: 1px solid black;
    position: relative;
    overflow: hidden;
}
h1 {
    margin: 0;
    padding: 0;
    display: inline;
    position: relative;
}
.line {
    margin-top: 10px;
    position: absolute;
    float: left;
    display: inline-block;
    height: 20px;
    width: 100%;
    background: blue;
}